Change the way Perl modules are installed, update the default Perl to 5.18.
Before, we had:
site_perl : lib/perl5/site_perl/5.18
site_perl/perl_arch : lib/perl5/site_perl/5.18/mach
perl_man3 : lib/perl5/5.18/man/man3
Now we have:
site_perl : lib/perl5/site_perl
site_arch : lib/perl5/site_perl/mach/5.18
perl_man3 : lib/perl5/site_perl/man/man3
Modules without any .so will be installed at the same place regardless of the

Lots and lots of cleanups. Teach p5-* in general about PKGNAMEPREFIX. Add
some missing/wrong dependencies. Show how to respect CC/CFLAGS. Many
miscellaneous modifications. I used more excessive hacks to force p5-Jcode
and p5-WWW-Search to respect CC/CFLAGS.